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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Wind speed predictions: Are we at the limit of our knowledge or can we improve?' taking place on Wednesday, 12 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Gregor Giebel DTU Wind Energy, Denmark
Gregor Giebel (1) F P Tuhfe Göcmen (1) Poul Sørensen (1) Niels Kjølstad Poulsen (2) Mahmood Mirzaei (2) Jesper Runge Kristoffersen (3)
(1) DTU Wind Energy, Risø, Denmark (2) DTU Compute, Lyngby, Denmark (3) Vattenfall, Fredericia, Denmark

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PossPOW: possible power of downregulated offshore wind power plants


Recently, offshore wind farms are designed as wind power plants, expected to contribute to the stability of the grid by offering ancillary services. One of those services is reserve power, achieved by down-regulating the wind farm from its possible (or available) power. Reliable methods exist to determine the available power of an individual turbine. However, the sum of those available powers is more than the available power of the wind farm simply because a turbine in the wake of a downregulated turbine sees more wind than would be available without the downregulation, due to decreased wake effects.


To be able to estimate the available power of a whole wind farm, models from various disciplines, including wake modeling of large offshore wind farms, aerodynamic models for wind turbines, stochastic model estimation and computer simulations have to be considered. During the project, the findings will be verified on some of the large offshore wind farms owned by Vattenfall, and possibly in a DONG Energy wind farm too. Dedicated experiments to the wind flow in large offshore wind farms are planned.

Main body of abstract

The first phase of the project is to estimate the effective (or rotor) wind speed of the turbines in a wind farm using power output together with rotational speed and pitch angle configurations as inputs. The modeling of power coefficient is crucial at that point since the turbine is no longer operating in optimum conditions during downregulation.
Additionally, wake modeling is necessary in order to take into account the change in wakes when the wind farm is down regulated. The PossPOW project will not develop new wake models, but the existing models, developed at DTU, will be re-parameterized for smaller averaging times approaching real time. The resulting model will use the effective wind speed and direction of the upstream turbines, estimate the corresponding velocity deficit, and calculate the available power of a wind farm during down regulation. The model will be verified using dedicated measurements at offshore wind farms. Eventually, consensus among TSOs for the acceptance of the technology will be attempted using dissemination and workshops.


Currently, Transmission System Operators (TSOs) have no real way to determine exactly the possible power of a down-regulated wind farm. Therefore, the aim of the PossPOW project is to develop a verified and internationally accepted way to determine the possible power of a down-regulated offshore wind farm. Project partners are DTU, Vestas, Siemens, Vattenfall and DONG.

Learning objectives
From this poster, readers will learn that the estimation of available power of downregulated offshore wind farms is not solved, that we have an approach, and a project to verify it. There will be dissemination towards TSOs, and possibly standardization.